There is a bug in the Radix javascript library that causes a plain text (unencrypted) message that starts with the digit 1 to be incorrectly be identified as an encrypted message.
For example, the message 1 ring to rule them all would be incorrectly interpreted as being an encrypted message.
This is a display bug only. The actual on-ledger data is correctly saved as plain text and will display correctly in the wallet and explorer when the Radix javascript library is fixed.
Workaround:
Do not start messages with the digit 1 until the Radix javascript library is updated.